Which Years Was The LML Duramax Diesel Engine Made?

Before GM introduced its L5P turbodiesels, there was a standout engine that featured enhanced fuel economy and greater dependability than previous iterations from the automaker. The GM LML Duramax Diesel was a sizeable 6.6 liters and was made from 2011 through 2016, available in select Chevy Silverado and GMC Sierra trucks. This brawny brute could generate just under 400 horsepower and over 760-pound feet of torque using design elements like a Variable Vane Turbo system.

The LML Duramax was born because of tightening emissions requirements, so it included a diesel particulate filter and the new SCR (selective catalytic reduction) system, meant to help lower nitrogen oxide fumes. Opinions on this engine are divided, with some considering it strong and reliable, while others don't consider the LML one of the best years for the 6.6 Duramax engine. This engine's Achilles' heel was its new high-pressure injection pump, which had a habit of failing. Nevertheless, according to Motor Trend, GM built over 600,000 LML Duramax diesels during the engine's lifespan.

GM switched from a CP3 pump used in previous engine iterations to the CP4 in the LML so that drivers could utilize alternative fuels like biodiesel. Biodiesel provides significant advantages in terms of lowered emissions, according to the U.S. Department of Energy. Unfortunately, the LML Duramax experienced serious problems when the CP4 pump malfunctioned, with issues like contaminants flooding the fuel system. Repairs following a pump failure could include new injectors, which meant some owners were out $10,000 to fix the issue, per Merchant-Automotive.com.

The reason this pump experienced so much trouble had to do with a lack of engine lubrication. Something you might not know about diesel engines is that they reduce friction via fuel. While the CP4.2 pump proved to be more efficient than previous versions, it couldn't properly lubricate the LML Duramax. Fortunately, some quick-thinking truck owners were able to head off the problem with CP3 aftermarket kits. However, if you experience a pump failure within 100,000 miles, the issue is covered under the GM warranty.

While there are certainly many truck owners who experienced a pump issue, leading to a class action lawsuit in that regard, there are also many drivers who tell a different story. For example, one individual asked the Duramax Forum community whether he should consider an LML because of the CP4 trouble, and the responses were interesting. One owner stated it was fine as long as you didn't run the fuel down past a quarter of a tank. Another echoed that thousands of CP4s appear to run problem-free, with one owner theorizing that the failure rate was likely around 5%. 

According to DirtyDieselCustom.ca, there are some straightforward tips to help keep an LML Duramax diesel in top shape, including using well-known gas stations and regularly changing your filter with a high-quality replacement. Not all fuel is equal, as you have branded and unbranded varieties with differing diesel fuel additives that can affect efficiency and performance.